I am looking at buying either a 2001/2002 WRX or a 2003 WRX but i am a little confused as everywhere i look has different performance figures, the subaru website says 6.3 for a 2001 WRX and 5.6 for a 2003 WRX but other places say completely different figures, so which is right?

Are there any big differences between the 2001 and 2003 WRX?

Also what insurance group is a 2001/2002 WRX and also a 2003 WRX as i have seen places which say anything from group 17 to group 20.